Rolling Mill for Rolling a Metallic Strip

ABSTRACT

In a rolling mill for rolling metal strip ( 1 ), especially steel strip, which has at least one rolling stand ( 2 ), an upstream coiler ( 3 ), and a downstream coiler ( 4 ), wherein an “S” roll unit ( 5, 6 ), which has two rolls ( 7, 8; 9, 10 ) that guide the strip ( 1 ) in the form of an “S”, is arranged between the upstream coiler ( 3 ) and the rolling stand ( 2 ) and/or between the rolling stand ( 2 ) and the downstream coiler ( 4 ), the invention provides that a first roll ( 7, 9 ) of the “S” roll unit ( 5, 6 ) is arranged in a fixed manner, and a second roll ( 8, 10 ) of the “S” roll unit ( 5, 6 ) is arranged in such a way that it can move relative to the first roll ( 7, 9 ).

The invention concerns a rolling mill for rolling metal strip,especially steel strip, which has at least one rolling stand, anupstream coiler, and a downstream coiler, wherein an “S” roll unit,which has two rolls that guide the strip in the form of an “S”, isarranged between the upstream coiler and the rolling stand and/orbetween the rolling stand and the downstream coiler.

The increasing necessity for weight savings, especially in theautomobile industry, has led to the development and use of load-adaptedparts, so-called tailored blanks. The essential feature of these partsthat is of special importance in this connection is that they have avariable thickness. Tailored blanks-were originally produced mainly bywelding. However, it was found that they can also be produced in anespecially favorable way by flexible cold rolling, which can be used toproduce tailored blanks.

In flexible cold rolling, the thickness of the rolling stock is variedduring rolling. In this regard, the roll gap can be periodically varied.The thickness variation results in mass flow disturbances and tensionfluctuations, especially on the entry side of the rolling stand but alsoon the delivery side of the rolling stand. At the rolling speedsnecessary for profitable production, these mass flow disturbances andtension fluctuations can no longer be compensated by the dynamics of thecoiler motors, so that so-called dancer rolls are used between therolling stand and the coilers in installations of this type.

WO 03/008,122 A1 describes a solution of this type. It discloses a coldrolling mill for cold rolling metal strip, which has a single stand withmeans for adjusting the roll gap, a coiler for uncoiling the stripupstream of the single cold rolling stand, and a coiler for coiling thestrip downstream of the rolling stand. To achieve flexible rolling, astrip accumulator is arranged between the upstream coiler and therolling stand for controlling the mass flow and the strip tension. Thisstrip accumulator consists of at least three rolls. The middle roll isdesigned as a dancer roll and can be moved perpendicularly to thedirection of conveyance of the strip.

EP 1 121 990 A2 discloses a similar solution—but with the use of alarger number of rolls. The same is true of a design disclosed by JP10-034,204 A1.

The dancer rolls described in the cited documents are connected with alinear actuator, with which they can be moved perpendicularly to thedirection of conveyance of the strip under open-loop or closed-loopcontrol. The strip accumulator function that is essential for flexiblecold rolling can be fulfilled in this way.

DE 198 18 207 C2 and JP 60-231,516 disclose so-called loopers, i.e.,rolls which are applied to the strip fed to the rolling stand or carriedaway from the rolling stand, in order, for example, to be able toundertake a determination of the tensile force in the strip.

During rolling, the rolling force can be reduced by tensile forces oneach side of the roll gap. However, it is only in the last pass that itmust not be too high, since otherwise, as is known from experience,problems can arise in the subsequent process steps, especially duringannealing. “S” roll units (“S” rolls) can be used to develop a tensiondifference between the rolling stand and coiler.

When both a strip accumulator function is to be realized, generally withdancer rolls, and a desired tension difference between the rolling standand the coiler is to be produced, generally by “S” roll units,considerable equipment expense is required in the prior-art solutions.

Therefore, the objective of the invention is to modify a metal striprolling mill of the aforementioned type in such a way that simple andthus economical means can be employed both to realize a stripaccumulator function, especially in the case of flexible rolling, and tomaintain a tension difference between the rolling stand and coilers thatcan be controlled in a well-defined way.

In accordance with the invention, this objective is achieved byarranging a first roll of the “S” roll unit in a fixed manner andarranging a second roll of the “S” roll unit in such a way that it canmove relative to the first roll.

Apart from guide rolls for the strip that may additionally be present,only the “S” roll unit is intended, in accordance with the invention, tobe provided between the coiler and rolling stand, but both the stripaccumulator function can be provided and the required tension on thestrip can be exerted with the proposed design of the “S” roll unit.

In a preferred embodiment, the second roll, which can move relative tothe first roll, is rotatably mounted on a swivel arm, which is supportedat one end in a stationary axis. The two axes of the rolls of the “S”roll unit are arranged parallel to each other. It is advantageous forthe stationary axis to coincide with the axis of rotation of the firstroll.

To swivel the second roll relative to the first roll, a linear actuatorarticulates with the swivel arm, preferably in a pivot some distancefrom the stationary axis. It is advantageous to use a hydraulicpiston-cylinder system as the linear actuator.

To be able to influence the development of tension in the strip in anoptimum way, means can be provided for driving at least one of the rollsof the “S” roll unit.

The proposal of the invention can be used to advantage in a cold rollingmill. In addition, the rolling stand is preferably a single stand. Theproposed system is suitable especially for flexible rolling, which iswhy the rolling stand can have means for flexible adjustment of the rollgap.

Finally, strip conveyance or handling is improved by equipping at leastone of the coilers with means that allow rotational speed control.

The proposed system makes it possible in a very simple and thusinexpensive way to provide a rolling plant for flexible rolling thatmakes available a strip accumulator, which is essential in this type ofoperation. In addition, the strip is also maintained at the requiredtension, so that the rolling itself can be carried out in anadvantageous way from the standpoint of process engineering.

A specific embodiment of the invention is illustrated in the drawings.

FIG. 1 shows a schematic side view of a rolling mill for the flexiblerolling of metal strip.

FIG. 2 shows an enlarged view of an “S” roll unit on the discharge sideof the rolling mill.

FIG. 1 shows a schematic view of a rolling mill, in which a coiled steelstrip 1 is uncoiled from an upstream coiler 3 and fed to a single coldrolling stand 2. Another coiler 4, which re-coils the rolled metal strip1, is installed downstream of the rolling stand 2 in the direction ofconveyance R of the metal strip 1. The coilers 3, 4 are provided withdrives (not shown), so that the strip 1 can be uncoiled and coiled underopen-loop or closed-loop control.

Flexible cold rolling of the strip is carried out in the rolling stand2. The strip 1 has a nonconstant thickness—as viewed in its longitudinaldirection. This means that, during the rolling process, the roll gap isvaried in accordance with a preset profile to produce a strip whosethickness varies periodically.

To allow this process to be carried out under conditions that arefavorable from the standpoint of process engineering, it is necessary tocompensate the change in mass flow in the strip that results from thevariable strip thickness. Furthermore, a well-defined tension must bedeveloped and maintained in the strip 1 to keep the rolling force low.

To accomplish this, an “S” roll unit 5, 6 is installed between theupstream coiler 3 and the rolling stand 2 and between the rolling stand2 and the downstream coiler 4, respectively. Each “S” roll unit has tworolls 7, 8 and 9, 10, respectively, which are arranged relative to eachother in a well-known way, so that the strip 1 is guided in an S-shapedpath. The resulting wrapping of the rolls 7, 8, 9, 10 makes it possible,with suitable driving of the rolls, to transmit a force to the strip 1and thus to maintain the desired tension in the strip 1 between the “S”roll unit 5, 6 and the rolling stand 2.

To be able to achieve both the application of tension in the strip andthe strip accumulator function, the “S” roll units 5 and 6 areconstructed as shown in FIG. 2. Each unit has one roll 9 (or 7) thatfeeds the strip 1 to or guides it away from the rolling stand 2. Thisroll 9 (or 7) is supported in a fixed position. By contrast, the otherroll 10 (or 8), is movably supported and can swivel relative to thefirst roll 9, 7. To this end, it is mounted at the end of a swivel arm11. The other end of the swivel arm 11 is supported in a stationary axis12, which coincides with the axis of rotation of the first roll 9, 7.

One end of a linear actuator 14, which is realized as a hydraulicpiston-cylinder system, articulates with the swivel arm, namely, in apivot 13 some distance from the axis of rotation of the second roll 8,10. The actuator 14 is supplied with hydraulic oil as indicated in FIG.2.

When the piston-cylinder system 14 is acted upon by hydraulic oil underopen-loop or closed-loop control, the pivot 13 can be raised or lowered,so that the second roll 8, 10 can be swiveled about its axis of rotation12. This results in a longer or shorter distance for the strip 1 betweenthe rolling stand 2 and coilers 3 or 4, thereby enabling the “S” rollunits 5, 6 to carry out a strip accumulator function.

The above-described construction of the rolling mill and especially ofthe two “S” roll units 5, 6 makes it possible, with a very simpledesign, to compensate the mass flow variation that occurs duringflexible cold rolling and at the same time to develop the tensiondifference between the rolling stand 2 and coilers 3, 4 that allows anoptimum rolling operation. With suitably fast automatic control of thelinear actuator 14, it is possible to compensate the mass flowdisturbances without any appreciable tension fluctuations.

To achieve this goal in the past, it was necessary to use a large numberof rolls, which made these installations expensive.

As a result of the compensation of the mass flow disturbances and theassociated reduction of the tension fluctuations, the automatic controlof strip thickness can be improved. It becomes possible to makeadjustments of the tensile stresses favorable for the rolling processwithout regard to the tensile stresses present at the coilers.

The compensation of the mass flow disturbances and the strip accumulatorfunction are now realized in one piece of equipment, namely, the “S”roll unit described above, for which separate pieces of equipment werepreviously needed.

List of Reference Symbols

-   1 metal strip (steel strip)-   2 rolling stand-   3 upstream coiler-   4 downstream coiler-   5 “S” roll unit-   6 “S” roll unit-   7 roll-   8 roll-   9 roll-   10 roll-   11 swivel arm-   12 stationary axis-   13 pivot-   14 linear actuator-   R direction of conveyance of the strip

1. Rolling mill for rolling metal strip (1), especially steel strip, which has at least one rolling stand (2), an upstream coiler (3), and a downstream coiler (4), wherein an “S” roll unit (5, 6), which has two rolls (7, 8; 9, 10) that guide the strip (1) in the form of an “S”, is arranged between the upstream coiler (3) and the rolling stand (2) and/or between the rolling stand (2) and the downstream coiler (4), characterized by the fact that a first roll (7, 9) of the “S” roll unit (5, 6) is arranged in a fixed manner, and a second roll (8, 10) of the “S” roll unit (5, 6) is arranged in such a way that it can move relative to the first roll (7, 9).
 2. Rolling mill in accordance with claim 1, characterized by the fact that the second roll (8, 10), which can move relative to the first roll (7, 9), is rotatably mounted on a swivel arm (11), which is supported at one end in a stationary axis (12).
 3. Rolling mill in accordance with claim 2, characterized by the fact that the stationary axis (12) coincides with the axis of rotation of the first roll (7, 9).
 4. Rolling mill in accordance with claim 2 or claim 3, characterized by the fact that a linear actuator (14) articulates with the swivel arm (11) in a pivot (13) some distance from the stationary axis (12).
 5. Rolling mill in accordance with claim 4, characterized by the fact that the linear actuator (14) is a hydraulic piston-cylinder system.
 6. Rolling mill in accordance with any of claims 1 to 5, characterized by means for driving at least one of the rolls (7, 8, 9, 10) of the “S” roll unit (5, 6).
 7. Rolling mill in accordance with any of claims 1 to 6, characterized by the fact that it is designed as a cold rolling mill.
 8. Rolling mill in accordance with any of claims 1 to 7, characterized by the fact that the rolling stand (2) is a single stand.
 9. Rolling mill in accordance with any of claims 1 to 8, characterized by the fact that the rolling stand (2) is equipped with means for flexible adjustment of the roll gap.
 10. Rolling mill in accordance with any of claims 1 to 9, characterized by the fact that at least one of the coilers (3, 4) is equipped with means for rotational speed control. 